Lithium secondary battery

ABSTRACT

A lithium secondary battery comprising a positive electrode composed of a positive electrode active material comprising an oxide compound comprising at least Li and Ni, and a negative electrode comprising an Li--Ag--Te alloy, a positive electrode active material for a lithium secondary battery, which is composed of an oxide compound represented by the formula: LiNi w  Al x  P y  O z  wherein 0.80&lt;w&lt;1.10, 0&lt;x&lt;0.015, 0&lt;y&lt;0.03 and 1.8≦z≦2.2, and a lithium secondary battery comprising said positive electrode active material. The lithium secondary battery of the present invention shows large charge-discharge capacity, high energy density, less degradation by the repetitive charge-discharge and is superior in cycle property. The positive electrode active material of the present invention, which is composed of an oxide compound represented by the formula: LiNi w  Al x  P y  O z  is economical and superior in the supply of starting materials, and the lithium secondary battery comprising said positive electrode active material is advantageous in that it has high capacity, is superior in cycle property and can be prepared stably at low costs.

TECHNICAL FIELD

The present invention relates to a lithium secondary battery having highcapacity and superior cycle property, a positive electrode activematerial to be used for lithium secondary battery, and to a positiveelectrode material compound.

BACKGROUND ART

In general, a lithium secondary battery is required to have (1) highenergy density (2) high output density (3) small self discharge ratio(4) economical aspect (5) high energy efficiency and (6) long cyclelife.

As a secondary battery having such properties, a nonaqueous electrolytebattery utilizing an electric energy produced by the migration oflithium ions, i.e., so-called lithium secondary battery, is known tohave high voltage and high energy density.

A lithium secondary battery comprising pure lithium as a negativeelectrode material can achieve high energy density of the negativeelectrode, whereas it suffers from a tendency to grow dendrite. Anelectrodeposition of metals generally proceeds in two steps of migrationof metallic ions to the electrode surface (i.e. diffusion) and receiptand release of electrons at the electrode (i.e. electrode reaction). Inthe electrodeposition of pure lithium, the electrode reaction proceedsquickly and the speed of lithium diffusing toward the electrode surfacedetermines the rate of electrodeposition. An electrodeposition whereinthe rate is determined by such mass migration often suffers from thegrowth of dendrite. The dendrite is a branch-like crystal which growsquickly once formed, and penetrates a separator, as a result of which itcauses short-circuit between the negative electrode and the positiveelectrode. Consequently, problems are caused which are undesirable interms of safety, such as combustion, markedly short cycle life of thebattery and poor cycle property.

On the other hand, a negative electrode composed of a lithium alloycomprising an intermetallic compound of Li and Al, Bi, Pb, Sn, In or thelike is known to suppress deposition of lithium in a dendrite state,since the speed of absorption of lithium in the negative electrodebecomes higher. However, this also poses problems in that the negativeelectrode becomes weak, so that it develops cracks through swelling andcontraction in volume which occur along with the absorption and releaseof lithium, to ultimately result in pulverulent negative electrode, andthat the electromotive force of the battery decreases due to a higherpotential of the electrode than that possessed by the negative electrodecomposed of pure lithium.

In an attempt to provide a lithium secondary battery free from suchproblems of dendrite and the like, a lithium ion battery using anegative electrode prepared from a carbon material has been produced.However, the lithium ion battery of this construction is associated witha defect that the discharge capacity becomes small.

A variety of materials have been conventionally considered to bepotential positive electrode active materials for lithium secondarybatteries, and typically included therein are inorganic compoundscapable of reversely inserting and eliminating lithium ions. As suchinorganic compounds, chalcogen compounds such as oxides and sulfideshave been mostly studied, and oxides having high potential, which arecapable of achieving a high energy density of batteries, have been foundto be particularly promising.

An example of the positive electrode active material comprising theabove-mentioned oxide is LiCoO₂. LiCoO₂ is a 4V class positive electrodeactive material reported by Mizushima et al. in 1980 (Mat. Res. Bull.,Vol. 15, pp 783-789) and mainly used as a positive electrode activematerial for lithium secondary batteries which are being used as a mainpower source of portable equipments currently put to use. Again, apositive electrode active material using such LiCoO₂ is inferior in thesupply of materials since Co is expensive.

Accordingly, an object of the present invention is to solve theabove-mentioned problems and provide a lithium secondary battery havinggreat charge-discharge capacity and superior cycle property. Anotherobject of the present invention is to provide a positive electrodeactive material for lithium secondary battery and a positive electrodematerial compound, which are free of the above-mentioned problems andwhich are economical, superior in suppliability, have greatcharge-discharge capacity and superior in cycle property.

DISCLOSURE OF THE INVENTION

The present inventors have conducted various studies taking note of thematerials of positive and negative electrodes of lithium secondarybattery, and found that the above-mentioned problems can be solved byusing, as a positive electrode active material, an oxide compoundcontaining at least lithium and nickel, and an Li--Ag--Te alloy as anegative electrode material. In particular, it has been found that theaddition of Al and P to an LiNiO₂ substance to afford the substance aspecific ratio of Ni, Al and P results in the provision of a positiveelectrode active material superior in capacity and cycle property. Thepresent invention has been made based on this finding.

That is, the present invention relates to a lithium secondary batterycomprising a positive electrode composed of a positive electrode activematerial comprising an oxide compound which comprises at least Li andNi, and a negative electrode comprising an Li--Ag--Te alloy; wherein thepositive electrode active material is composed of an oxide compoundcomprising, besides Li and Ni, at least one member selected from thegroup consisting of Co, Fe, Cr, V, Mn, P, Al, In, Sn, Ti, Cu, Ga, Ag andZn; a lithium secondary battery wherein the positive electrode activematerial is composed of an oxide compound represented by the formulaLiNi_(w) Al_(x) P_(y) O_(z) wherein 0.80<w<1.10, 0<x<0.015, 0<y<0.03 and1.8≦z≦2.2; a lithium secondary battery wherein the atomic ratio of theLi--Ag--Te alloy is Li:Ag:Te=10-120:1-20:0.001-2; and a lithiumsecondary battery wherein the negative electrode is composed of anLi--Ag--M1--M2--Te alloy wherein M1 is at least one member selected fromthe metals of 3A, 4A and 5A group metals in the periodic table (longperiod), and M2 is at least one member selected from transition metalsexcept Ag; and in particular, the above-mentioned lithium secondarybattery wherein the atomic ratio of the Li--Ag--M1--M2--Te alloy isLi:Ag:M1:M2:Te=10-120:1-30:1-100:1-30:0.001-2.

The present invention also relates to a positive electrode activematerial for lithium secondary battery, which is composed of an oxidecompound represented by the formula: LiNi_(w) Al_(x) P_(y) O_(z) wherein0.80<w<1.10, 0<x<0.015, 0<y<0.03 and 1.8≦z≦2.2, a positive electrodematerial compound comprising the above-mentioned positive electrodeactive material, a conductive agent and a binder, and a lithiumsecondary battery comprising the above-mentioned positive electrodeactive material.

The present invention further relates to a lithium secondary batterycomprising a positive electrode composed of a positive electrode activematerial comprising an oxide compound represented by the formula:LiNi_(w) Al_(x) P_(y) O_(z) wherein 0.80<w<1.10, 0<x<0.015, 0<y<0.03 and1.8≦z≦2.2, a negative electrode composed of an Li--Ag--M1--M2--Te alloywherein M1 is at least one member selected from the metals of 3A, 4A and5A group metals in the periodic table (long period), and M2 is at leastone member selected from transition metals except Ag, and a nonaqueouselectrolyte.

The positive electrode active material in the present invention isexemplified by those composed of an oxide compound containing at leastLi and Ni. Said oxide compound may be a known compound, with preferencegiven to those represented by the following formulas:

(1) Li_(p) Ni_(q) O₂ (0<p≦1, 0<q≦1)

(2) LiNi₁₋ _(r) M_(r) O₂ (0<r<1) (e.g. LiNi₁₋ _(r) Co_(r) O₂ wherein0<r<1)

(3) Li_(s) NiM_(t) O₂ (0.1≦s≦1.2, 0.001≦t≦0.2) (e.g. LiNiM_(t) O₂wherein 0.001≦t≦0.2) and

(4) Li_(u) Ni₁₋ _(v) M_(v) O₂ (0.1≦u≦1.2, 0.001≦v≦0.2) (e.g. LiNi₁₋ _(v)M_(v) O₂ wherein 0.001≦v≦0.2).

In the above formulas, M is one or more metals selected from the groupof Co, Fe, Cr, V, Mn, P, Al, In, Sn, Ti, Cu, Ga, Ag and Zn.

Specific examples of the oxide compound include LiNiO₂, LiNi₀₅ Co₀₅ O₂,LiNi₀₇₅ Co₀₂₅ O₂, LiNi₀₂₅ Co₀₇₅ O₂, LiNi₀₉₉₅ Fe₀₀₀₅ Fe₀₀₀₅ O₂, LiNi₀₉₉Cr₀₀₁ O₂, LiNi₀₉₅ V₀₀₅ O₂, LiNi₀₉₂ Mn₀₀₈ O₂, LiNiP₀₀₅ O₂, LiNiAl₀₀₈ O₂,LiNiIn₀₀₀₅ O₂, LiNi₀₉₅ Sn₀₀₅ O₂, LiNi₀₉₉ Ti₀₀₁ O₂, LiNi₀₉₅ Cu₀₀₅ O₂,LiNiGa₀₀₀₅ O₂, LiNiAg₀₁ O₂ and LiNiZn₀₁₅ O₂.

The above-mentioned oxide compound can be obtained by mixing apredetermined amount of lithium salt (e.g. lithium carbonate, lithiumsulfate and lithium nitrate), lithium oxide, or lithium hydroxide andthe like, and nickel salt (e.g. nickel carbonate, nickel sulfate, nickelnitrate and nickel oxyhydroxide), nickel oxide or nickel hydroxide andthe like, and where necessary, one or more salts (e.g. carbonate,sulfate and nitrate), oxides or hydroxides of metal selected fromcobalt, iron, chromium, vanadium, manganese, phosphorus, aluminum,indium, tin, titanium, copper, gallium, silver and zinc, andheat-sintering the mixture at 600°-900° C., preferably 650°-800° C. Theabove-mentioned oxide compound can be also prepared using halidesbesides salts, oxides and hydroxides of metal such as lithium andnickel.

Particularly preferable positive electrode active material is thatcomposed of a novel oxide compound represented by the formula: LiNi_(w)Al_(x) P_(y) O_(z) wherein 0.80<w<1.10, 0<x<0.015, 0<y<0.03 and1.8≦z≦2.2.

In the oxide compound represented by the above-mentioned formula:LiNi_(w) Al_(x) P_(y) O_(z), the range of w is 0.80<w<1.10, preferably0.95<w<1.05. When w is in the above-mentioned range, the battery comesto have more superior capacity and cycle property. The range of x is0<x<0.015, preferably 0.001<x<0.010. When x is in the above-mentionedrange, the battery comes to have more superior capacity and cycleproperty. The range of y is 0<y<0.03, preferably 0.001<y<0.015. When yis in the above-mentioned range, the battery comes to have more superiorcapacity and cycle property. The range of z is 1.8≦z≦2.2, preferably1.9≦z≦2.1. When z is in the above-mentioned range, the battery suffersless from oxygen deficiency or products from side reaction, and thebattery becomes more superior in capacity and cycle property.

The oxide compound represented by the formula: LiNi_(w) Al_(x) P_(y)O_(z) is obtained by, for example, subjecting a predetermined amount ofa mixture of single unit compounds of lithium, nickel, aluminum andphosphorus, or salts thereof (e.g. carbonate, sulfate and nitrate),oxides thereof or hydroxides thereof, and metallic organic compounds tosintering (e.g. heating temperature: about 600°-900° C., preferably650°-800° C.), solid phase method, sol-gel method, CVD, PVD, thermalspraying, thermal decomposition or the like.

The respective oxide compounds thus obtained are generally pulverized inmortar, ball mill, hammer mill, jet mill and the like to prepare powdersof about 0.1-20 μm in average particle size, and used as positiveelectrode active materials.

A positive electrode for lithium secondary battery can be prepared as inthe following using the above-mentioned positive electrode activematerial. For example, a binder such as fluorocarbon resin (e.g.polyvinylidene fluoride and polytetrafluoroethylene),polyethylene andethylene-propylene-diene polymer (EPDM) and conductive material such asacetylene black, ketzen black and graphite are added to theabove-mentioned positive electrode active material to give a positiveelectrode material compound. This material compound can be formed into asuitable shape and size by an optional method such as doctor blademethod, cast forming, compression forming and roll forming to give apositive electrode for lithium secondary battery. In this way, apositive electrode having a layer or tunnel crystal structure allowingentrance and exit of lithium ions can be prepared. In the case of apositive electrode sheet, it preferably has a thickness of 50-500 μm.The binder is preferably a fluorocarbon resin.

When a binder and a conductive agent are added, their contents are about1-10 parts by weight and about 3-15 parts by weight, respectively, bothper 100 parts by weight of the above-mentioned positive electrode activematerial.

When, for example, doctor blade method is employed, about 10-300 partsby weight of a solvent such as N-methyl-2-pyrrolidone, propylenecarbonate, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), xyleneand cyclohexane is mixed with 100 parts by weight of the above-mentionedpositive electrode material compound to give a positive electrode paste.

The material for the negative electrode of the lithium secondary batteryof the present invention may be a conventionally-known material fornegative electrodes. Examples thereof include lithium, alloy thereof,carbon material and oxides such as Nb₂ O₅ and Fe₂ O₃, with preferencegiven to lithium alloy.

When a lithium alloy is used, it is preferably contained in an atomicproportion of 10% or more, more preferably 10-50%. When the content oflithium is not less than 10%, a decrease in capacity or battery voltagecaused by alloying can be suppressed.

Examples of the above-mentioned lithium alloy include Li--Ag--Te alloys,namely, Li--Ag--Te alloys containing at least Li, Ag and Te.

In the Li--Ag--Te alloy, Ag reacts with lithium to form a lithium alloywhich functions to absorb or release lithium during charging ordischarging. Te forms a stable intermetallic compound Ag_(a) Te_(b) withthe above-mentioned Ag, and Li₂ Te with lithium.

These intermetallic compounds make crystal particles of negativeelectrode alloy extremely fine, thereby markedly increasing the area ofgrain boundary. The speed of the diffusion of lithium in the grainboundary reaches not less than several dozen times higher thantransgranular speed, so that the lithium electrodeposition is lessrate-determined by diffusion of Li, whereby growth of dendrite issuppressed. This also results in an enhanced efficiency of absorptionand release of lithium.

These intermetallic compounds accumulate in grain boundary to form athree-dimensional shell. Of the above-mentioned intermetallic compoundsAg_(a) Te_(b) and Li₂ Te, Ag_(a) Te_(b) functions as an aggregate toretain the strength of the shell, or a binder of Li₂ Te. The speed oflithium diffusing in Li₂ Te is notably high, so that Li₂ Te functions asa high speed diffusion path of lithium, whereby the absorption andrelease of Li during charging and discharging of the battery proceedthrough said shell. In addition, the growth of dendrite is suppressed,since said shell is formed from the above-mentioned intermetalliccompound. The shell also functions as a barrier of Ag diffusion, wherebyfallout of Ag from the electrode during discharge can be prevented. Theequivalent electrode potential of Li₂ Te and lithium leads to anequivalent electromotive force of a battery comprising Li₂ Te and abattery comprising pure lithium.

The above-mentioned Li--Ag--Te alloy preferably has an atomic ratio,Li:Ag:Te of 10-120:1-20:0.001-2, more preferably Li:Ag:Te=10-80:5-20:0.01-0.5.

An atomic ratio of Ag within the above-mentioned range relative to theatomic ratio of Li is preferable in that crystal particles can be madesufficiently fine; sufficient strength of the shell composed of theintermetallic compounds can be achieved; the alloy is easily processedinto a sheet; and the battery is afforded a high electromotive force. ATe having an atomic ratio within the above-mentioned range relative tothe atomic ratio of Li is preferable in that dendrite can besufficiently suppressed; crystal particles can be made sufficientlyfine; the alloy is easily processed into a sheet; and the battery isafforded a high electromotive force.

Of the above-mentioned Li--Ag--Te alloys, an Li--Ag--M1--M2--Te alloywherein M1 is at least one member selected from 3A, 4A and 5A groupmetals in the periodic table (long period), and M2 is at least onemember selected from transition metals except Ag, is particularlypreferable. In the present invention, transition metal includes 3A-7A,8, 1B and 2B group metals in the periodic table (long period).

The Li--Ag--M1--M2--Te alloy has the same advantages as those possessedby the above-mentioned Li--Ag--Te alloy, and respective alloy componentsof M1 and M2 function as an Li diffusion promoter and a binder,respectively, to more effectively suppress the growth of dendrite anddegradation caused by the swelling and contraction of negative electrodealong with absorption and release of lithium, as a result of which thecycle life of the battery is prolonged.

M1 in the above-mentioned Li--Ag--M1--M2--Te alloy is preferably one ormore members selected from Al, Si, In, Sn, Bi and Pb, more preferablyone or more members selected from In, Sn, Bi and Pb. M2 is preferablyone or more members selected from Zn, Fe, Co, Ni, Mn, Mo and W, morepreferably one or more members selected from Zn, Fe and Ni.

The aforementioned Li--Ag--M1--M2--Te alloy preferably has an atomicratio of Li:Ag:M1:M2:Te of 10-120:1-30:1-100:1-30:0.001-2, morepreferably 10-80:10-30:10-100:1-20:0.01-0.5.

An Li--Ag--M1--M2--Te alloy having an atomic ratio of Ag within theabove range relative to the atomic ratio of Li is advantageous in thatthe battery tends to achieve superior cycle property, high speed of Lidiffusion and high electromotive force. When the atomic ratios of M1 andM2 are in the above-mentioned range relative to the atomic ratio of Li,the respective alloy components of M1 and M2 exert sufficient Lidiffusion promoting effect and binding effect, thus leading to animproved cycle life, charge-discharge capacity, electromotive force andenergy density of the battery. When the atomic ratio of Te is within theabove-mentioned range relative to the atomic ratio of Li, the diffusionof Li is promoted and the cycle life of the battery desirably becomeslonger.

The lithium alloys such as the above-mentioned Li--Ag--Te alloy andLi--Ag--M1--M2--Te alloy are prepared, for example, according to asuitable known alloying method such as reaction of respective moltenalloy components in a predetermined ratios (melting method) and reactionon evaporation.

In the melting method, the alloy components are heated and melted in aninert gas atmosphere for alloying. The heating-melting is preferablyperformed at a temperature not less than the melting point of Li alloyto allow quick progress of the alloying reaction.

The alloying by evaporation comprises evaporating the alloy componentsto solidify same on the surface of other kinds of metals. This methodallows production of a non-equilibrium phase alloy of high melting pointmetals which cannot be alloyed by the above-mentioned melting method,and low melting point metals. For evaporation, usable methods includevarious sputterings such as ion beam sputtering, electron beamevaporation, various ion platings, flash plasma evaporation, pulseplasma evaporation and CVD. When the aforementioned non-equilibriumphase alloy is prepared, a method comprising accelerating atoms or ionsin the direction of substrate for evaporation, such as ion plating andsputtering, is preferable.

The method of forming the negative electrode is not particularlylimited, and conventional methods can be employed. For example, anoptional method such as doctor blade method, cast forming, compressionforming and roll forming is employed to form a negative electrode in aknown form, such as sheet, tape, thin film and substrate (hereinafterthese forms are generally referred to as sheet form). A negativeelectrode sheet preferably has a thickness of 10-300 μm.

When a metallic material such as lithium and alloy thereof is used as anegative electrode material, for example, a method for forming anegative electrode material into a sheet by hot rolling or hotextrusion, and a method for forming a negative electrode material layeron a collector by hot dipping or low pressure plasma spraying may beused. The latter method of forming a negative electrode material layeron a collector is advantageous for forming a negative electrode sheetwherein such negative electrode material layer can be formed on one orboth sides of the collector.

The hot rolling comprises heating the metallic materials for goodprocessability and press-rolling the material, and the hot extrusioncomprises heating the metallic materials for good processability andextruding the material. The hot dipping comprises melting the metal inan inert gas and immersing a collector therein for plating, and the lowpressure plasma spraying comprises spraying a molten metal on acollector under a reduced pressure inert gas atmosphere (preferablyabout 10-100 Torr).

A negative electrode sheet can be also formed by, for example, settingnegative electrode material components onto a collector sheet by theaforementioned evaporation. In addition, a negative electrode sheetmaterial may be bonded to a collector sheet by a suitable method such asbrazing, soldering, ultrasonic welding, spot welding, press-adhesion androll press-rolling, whereby a negative electrode sheet can be formed.

The collector sheet refers to that composed of suitable conductors suchas Ni, Al, Cu, Ag and Fe. Specific examples thereof include metal foilsheet, metal mesh sheet and metal porous sheet.

A carbon material containing no Li can be directly used as a negativeelectrode, since the positive electrode active material contains Li inthe present invention.

Of the above-mentioned positive electrodes and negative electrodes, acombination of a positive electrode comprising a positive electrodeactive material composed of an oxide compound of the formula: LiNi_(w)Al_(x) P_(y) O_(z) and a negative electrode composed of anLi--Ag--M1--M2--Te alloy is particularly preferable.

The lithium secondary battery of the present invention comprises anelectrolyte. The electrolyte is generally a nonaqueous one, which isexemplified by electrolyte solutions obtained by dissolving varioussalts conventionally used for lithium batteries, in nonaqueous solvent,and solid electrolyte.

Examples of the above-mentioned salt include LiClO₄, LiBF₄, LiPF₄,LiPF₆, LiAsF₃, LiAsF₆, LiAlCl₄, Li(CF₂ SO₂)₂ and Li(CF₃ SO₂)₂ N.Examples of the nonaqueous solvent include ethylene carbonate, propylenecarbonate, dimethyl sulfoxide, sulfolane, γ-butyro-lactone,1,2-dimethoxyethane, N,N-dimethylformamide, tetrahydrofuran,1,3-dioxolane, 2-methyltetrahydrofuran, diethyl ether, dimethylcarbonate, diethyl carbonate, methyl formate, methyl acetate,acetonitrile, 3-methyl-2-oxazolidinone, ethylene glycol sulfite,dimethyl sulfite, nitromethane, N-methylpyrrolidinone and mixturesthereof.

The above-mentioned salts are dissolved in the above-mentionednonaqueous solvent to a concentration of about 0.1-3 moles/L and used asan electrolyte solution. Where necessary, an organic additive such as2-methylfuran, thiophene, pyrrole and crown ether may be dissolved insaid electrolyte solution. The electrolyte solution is generally usedupon impregnating or filling a separator such as porous polymer, glassfilter and nonwoven fabric with the same.

When the nonaqueous electrolyte is a solid electrolyte, theabove-mentioned salts are mixed with a polymer such as polyethyleneoxide, polyphosphazene, polyaziridine, polyethylene sulfide, polyvinylalcohol, and derivatives, mixtures and compounds thereof. Alternatively,the above-mentioned nonaqueous solvent may be incorporated intopolymers. Such solid electrolyte may also act as a separator between thepositive electrode and the negative electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of one embodiment of the lithium secondarybattery of the present invention.

FIG. 2 is a cross section of another embodiment of the lithium secondarybattery of the present invention.

FIG. 3 shows the relationship between the number of cycles and dischargecapacity in the charge-discharge test with regard to the respectivebatteries obtained in Example 1 and Comparative Example 1.

FIG. 4 shows discharge property curves with regard to the respectivebatteries obtained in Examples 1-17 and Comparative Example 1.

Referring to FIG. 1, 1 is a negative electrode tape, 2 is a positiveelectrode sheet, 3 is a separator, 4a is a negative electrode collector,4b is a positive electrode collector, 5 is a battery case, 6 is apositive electrode cap, 7 is a gasket, 8a is a negative electrode leadwire, and 8b is a positive electrode lead wire.

In FIG. 2, 11 is a positive electrode, 12 is a negative electrode, 13 isa separator, 14a and 14b are collectors, 15 is a positive electrode can,16 is a negative electrode cap and 17 is an insulator.

The lithium secondary battery of FIG. 1 has a structure wherein aseparator 3, a negative electrode tape 1, a separator 3 and a positiveelectrode sheet 2 are overlapped in this order, the obtained laminate iswound to form a spiral pattern with the positive electrode sheet 2located inside thereof and set in the battery case 5, and the batterycase 5 is applied with a positive electrode cap 6 and sealed with agasket 7.

The lithium secondary battery of FIG. 2 has a structure wherein aseparator 13 is interposed between the positive electrode 11 and thenegative electrode 12, and the positive electrode can 15 pressure-weldedto the outside of the positive electrode 11, and the negative electrodecap 16 pressure-welded to the outside of the negative electrode 12 aresealed with an insulator 17.

The shape of the lithium secondary battery of the present invention canbe determined as appropriate according to the object of use, and can bea tube type battery as shown in FIG. 1, a coin type battery as shown inFIG. 2, of a button type, square type, sheet type or paper type.

The materials of the elements besides the above-mentioned positiveelectrode and negative electrode may be conventional ones and aresubject to no particular limitation. Examples of the material of thepositive electrode cap and positive electrode can include stainlesscopper and aluminum. Examples of the material of the battery case andnegative electrode cap include stainless copper, nickel andnickel-plated iron. Examples of the material of the gasket and insulatorinclude polypropylene and polyethylene. Examples of the material ofnegative electrode lead wire include nickel and stainless steel, andexamples of the material of the positive electrode lead wire includealuminum and stainless steel.

The method for producing the afore-said lithium secondary battery is notsubject to particular limitation, and can be prepared by a known method.For example, a winding type tubular lithium secondary battery can bemanufactured by winding the above-mentioned positive electrode and thenegative electrode with a separator interposed between the twoelectrodes, housing same in a battery can, injecting an electrolytesolution and applying an insulation sealant at the edge of the batterycan. The coin type and button type lithium secondary batteries can bemanufactured in the same manner as above except that the positiveelectrode and the negative electrode with a separator interposed betweenthe two electrodes are housed in a battery can without winding.

The present invention is described in more detail by way of thefollowing Examples, to which the invention is not limited.

EXAMPLE 1 Preparation of Positive Electrode Active Material

Lithium nitrate (LiNO₃) and nickel hydroxide (Ni(OH)₂) were respectivelyweighed in an aluminum crucible at an atomic ratio of Li:Ni=1:1 andmixed. Then, the mixture was sintered in an electric furnace at 700° C.for 24 hours in an oxygen stream. The sintered substance thus obtainedwas determined by a powder X ray diffraction method. As a result, thesubstance coincided with JCPDS card No. 9-63 and was identified to beLiNiO₂ of space group R-3m. This LiNiO₂ was pulverized by planet typeball mill to give a positive electrode active material having a particlesize of not more than 20 μm.

Preparation of Positive Electrode

The above-mentioned positive electrode active material (90 parts byweight), acetylene black (7 parts by weight) as a conductive material,polyvinilidene fluoride (PVDF, 3 parts by weight) as a binder andN-methyl-2-pyrrolidone (NMP, 97 parts by weight) as a solvent werethoroughly mixed to give a paste. The paste was coated on one side of a20 μm thick, 39.5 mm wide aluminum sheet, dried in an electric furnaceat 200° C., from which an electrode sheet was continuously prepared. Thesame paste was coated on the other side of the sheet and dried to makethe total thickness 400 μm. The obtained electrode sheet was cut into a400 mm long piece and press-rolled to make the thickness 200 μm. A 20 mmlong coating layer was peeled off from one side and a lead wire waswelded thereto. The electrode was dried in a vacuum drier at 120° C. for3 hours to give a positive electrode sheet.

Preparation of Negative Electrode

A 2 μm thick Ni plating layer and then a 0.5 μm thick Ag plating layerwere formed on the entirety of a 41 mm wide, 10 μm thick copper tape byelectric plating, and a 20 μm thick Li--Ag--Te alloy layer was formed onthe obtained tape by melt-plating. As the Li--Ag--Te alloy, used was amixture of the respective components mixed at an atomic ratio ofLi:Ag:Te =90:10:0.1. For melt plating, the starting material mixed atthe above-mentioned atomic ratio was weighed in a stainless container,melted at 250° C. in an argon atmosphere and subjected to plating usinga squeezing type film thickness controller.

The obtained tape of the starting material was cut into 420 mm long tapeand used as a negative electrode tape.

Preparation of Battery

A size AA tubular lithium secondary battery as shown in FIG. 1 wasprepared in the following manner using the above-mentioned negativeelectrode tape, a 25 μm thick separator composed of a film with finepores made from polypropylene, and the above-mentioned positiveelectrode sheet.

A separator 3, a negative electrode tape 1, a separator 3 and a positiveelectrode sheet 2 were overlapped in this order, and wound to form aspiral pattern with the positive electrode sheet 2 located insidethereof. The spiral product was placed in a size AA nickel-plated Febattery case 5. Along therewith, a negative electrode lead wire 8aconnected to a negative electrode collector 4a in the negative electrodetape 1, which collector being composed of a copper tape applied withsilver and nickel platings, was welded to the inside bottom surface ofthe above-mentioned battery case 5, and a positive electrode lead wire8b connected to a positive electrode collector 4b in the positiveelectrode sheet 2, which collector being composed of aluminum sheet, waswelded to the positive electrode cap 6 in the above-mentioned batterycase 5. Then, an electrolyte solution (3 ml) was injected into thebattery case 5. A positive electrode cap 6 was applied onto the batterycase 5, and the battery was sealed with a gasket 7. As the electrolytesolution, a solution obtained by dissolving one mole of LiPF₆ in amixture of ethylene carbonate and diethyl carbonate (volume ratio 1:1)was used.

The above-mentioned size AA lithium secondary battery allows, uponconversion of the chemical energy produced inside, use of electricenergy from the both terminals at the positive electrode cap 6 and thebottom surface of the battery case 5.

COMPARATIVE EXAMPLE 1

In the same manner as in Example 1 except that the below-noted positiveelectrode and negative electrode were used, a size AA lithium secondarybattery was prepared.

Preparation of Positive Electrode

In the same manner as in Example 1, a positive electrode sheet wasprepared except that the length was set to 300 mm.

Preparation of Negative Electrode

Natural graphite (93 parts by weight), PVDF (7 parts by weight) as abinder, and NMP (93 parts by weight) as a solvent were thoroughly mixedto give a paste. In the same manner as in Example 1 for preparation of apositive electrode sheet, a 180 μm thick, 41 mm wide and 300 mm longnegative electrode sheet was prepared, except that a 10 μm thick coppersheet was used instead of the aluminum collector sheet.

EVALUATION TEST 1

Using the respective batteries obtained in Example 1 and ComparativeExample 1 above, a charge-discharge test was repeated as noted below.Charging was done according to the constant voltage method using 500 mAcurrent for 3 hours wherein the highest voltage limit was 4.2 V.Discharging was done until the lowest limit voltage became 2.75 V using100 mA current, and the capacity of each battery was determined. Acombination of one charging and one discharging was considered one cycleand the test included 50 cycles thereof.

The test results are shown in FIG. 3. As is evident from this graph, thebattery of Example 1 showed higher capacity than did the battery ofComparative Example 1 using a carbon material for the negativeelectrode. That is, the discharge capacity of the battery of Example 1was about 40% higher than that possessed by the battery of ComparativeExample 1. The discharge capacity of the battery of Example 1 scarcelychanged even after 50 cycles of repetitive charging and discharging.Although not shown in the Figure, the average discharge voltage then was3.6 V in Example 1 and 3.5 V in Comparative Example 1, showing higherdischarge voltage of the battery of Example 1. After 50 cycles of theabove-mentioned charge-discharge test, the battery of Example 1 wasdisassembled to examine the occurrence of dendrite in the negativeelectrode. As a result, no dendrite was found.

EXAMPLES 2-17

In the same manner as in Example 1 except that the positive electrodeactive material as shown in Table 1 was used for preparing a positiveelectrode, batteries were prepared. The positive electrode activematerials as used in Examples 5-17 were easily pulverized aftersintering, as compared with the positive electrode active material ofExample 1, thus enabling notable shortening of the preparation time ofthe positive electrode.

                  TABLE 1                                                         ______________________________________                                        Ex.  Positive electrode                                                                         Material of positive electrode                              No.  active material                                                                            active material                                             ______________________________________                                        2    LiNi.sub.0.75 Co.sub.0.25 O.sub.2                                                          lithium nitrate, nickel hydroxide,                                            basic cobalt carbonate                                      3    LiNi.sub.0.5 Co.sub.0.5 O.sub.2                                                            same as above                                               4    LiNi.sub.0.25 Co.sub.0.75 O.sub.2                                                          same as above                                               5    LiNi.sub.0.995 Fe.sub.0.005 O.sub.2                                                        lithium nitrate, nickel hydroxide, Fe(OH).sub.3             6    LiNi.sub.0.99 Cr.sub.0.01 O.sub.2                                                          lithium nitrate, nickel hydroxide,                                            Cr(NO.sub.3).sub.3.9H.sub.2 O                               7    LiNi.sub.0.95 V.sub.0.05 O.sub.2                                                           lithium nitrate, nickel hydroxide, NH.sub.4 VO.sub.3        8    LiNi.sub.0.92 Mn.sub.0.08 O.sub.2                                                          lithium nitrate, nickel hydroxide, MnCO.sub.3               9    LiNiP.sub.0.05 O.sub.2                                                                     lithium nitrate, nickel hydroxide,                                            phosphoric acid                                             10   LiNiAl.sub.0.08 O.sub.2                                                                    lithium nitrate, nickel hydroxide,                                            Al(NO.sub.3).sub.3.9H.sub.2 O                               11   LiNiIn.sub.0.005 O.sub.2                                                                   lithium nitrate, nickel hydroxide, In.sub.2 O.sub.3         12   LiNi.sub.0.95 Sn.sub.0.05 O.sub.2                                                          lithium nitrate, nickel hydroxide, SnO.sub.2                13   LiNi.sub.0.99 Ti.sub.0.01 O.sub.2                                                          lithium nitrate, nickel hydroxide,                                            Ti(O-i-C.sub.3 H.sub.7).sub.4                               14   LiNi.sub.0.95 Cu.sub.0.05 O.sub.2                                                          lithium nitrate, nickel hydroxide,                                            Cu(NO.sub.3).sub.2.3H.sub.2 O                               15   LiNiGa.sub.0.005 O.sub.2                                                                   lithium nitrate, nickel hydroxide,                                            Ga(NO.sub.3).sub.3.9H.sub.2 O                               16   LiNiAg.sub.0.1 O.sub.2                                                                     lithium nitrate, nickel hydroxide, AgNO.sub.3               17   LiNiZn.sub.0.15 0.sub.2                                                                    lithium nitrate, nickel hydroxide,                                            Zn(NO.sub.3).sub.2.6H.sub.2 O)                              ______________________________________                                    

The discharge property of the batteries of Examples 1-17 and ComparativeExample 1 is shown in FIG. 4. The discharge property of Examples 1-17 isexpressed by embracing all curves obtained in these Examples.

As is evident from FIG. 4, the average discharge voltage of therespective batteries of Examples was about 3.6 V and the batteries canbe incorporated into the equipments already in use.

COMPARATIVE EXAMPLE 2

In the same manner as in Example 1 except that pure lithium was used forthe negative electrode, a size AA tubular lithium secondary battery wasprepared.

The battery of Comparative Example 2 was subjected to 50 cycles ofcharge-discharge test and disassembled to examine the negativeelectrode. As a result, dendrite was found.

The lithium secondary battery of the present invention comprises apositive electrode composed of a positive electrode active materialcomprising an oxide compound containing at least lithium and nickel.Consequently, the positive electrode has an α-NaFeO₂ type crystalstructure which enables repetition of reversible release and absorptionof lithium ions by charge-discharge of the battery to result in highenergy density, as in the case of a known oxide compound (LiCoO₂) oflithium and cobalt which has been known to have high energy density. Thenegative electrode composed of a solid-solution type alloy containingLi--Ag--Te alloy functions to absorb and release Li during charging anddischarging to promote diffusion of Li during charging and discharging,and suppresses growth of dendrite.

In other words, since the lithium secondary battery of the presentinvention comprises, in combination, a high capacity positive electrodecomposed of a positive electrode active material comprising an oxidecompound containing at least lithium and nickel and a negative electrodecomposed of an Li--Ag--Te alloy capable of suppressing growth ofdendrite, the battery has high charge-discharge capacity, high energydensity and superior cycle property with less degradation caused byrepetitive charging and discharging.

EXAMPLE 21 Preparation of Positive Electrode Active Material

Lithium hydroxide monohydrate (LiOH·H₂ O), nickel hydroxide Ni(OH)₂ !,aluminum hydroxide Al(OH)₃ ! and lithium phosphate Li₃ PO₄ ! wereweighed to satisfy an atomic ratio of Li:Ni:Al:P=1:0.99:0.002:0.005 andthoroughly mixed in a mortar. The mixture was placed in an aluminumcrucible and subjected to heat treatment in an electric furnace at 700°C. for 24 hours in an oxygen stream. The substance obtained waspulverized in a mortar, classified by passing through a sieve to give apowdery positive electrode active material having a particle size of notmore than 20 μm.

EXAMPLES 22-34

In the same manner as in Example 21 except that the atomic ratio of Li,Ni, Al and P was varied as shown in Table 2, powdery positive electrodeactive materials were prepared.

COMPARATIVE EXAMPLE 11

In the same manner as in Example 21 except that lithium hydroxidemonohydrate (LiOH·H₂ O) and nickel hydroxide Ni(OH)₂ ! were weighed tosatisfy an atomic ratio of Li:Ni=1:1, a powdery positive electrodeactive material was prepared.

COMPARATIVE EXAMPLE 12-17

In the same manner as in Example 21 except that the atomic ratio of Li,Ni, Al and P was varied as shown in Table 2, powdery positive electrodeactive materials were prepared.

COMPARATIVE EXAMPLE 18

Lithium hydroxide monohydrate and nickel powder were mixed in amounts asshown in Table 2 and subjected to heat treatment at 750° C. for 12 hoursin an oxygen atmosphere. The substance obtained was pulverized andsubjected to a heat treatment under the same conditions. Thereafter, thesame steps as in Example 21 were followed to give a powdery positiveelectrode active material.

COMPARATIVE EXAMPLE 19

Lithium carbonate and cobalt carbonate were mixed in amounts as shown inTable 3 and subjected to heat treatment at 900° C. for 20 hours inatmosphere. The substance obtained was pulverized and subjected to aheat treatment under the same conditions. Thereafter, the same steps asin Example 21 were followed to give a powdery positive electrode activematerial.

COMPARATIVE EXAMPLE 20

Lithium carbonate, nickel oxide, stannic oxide and scandium oxide weremixed in amounts as shown in Table 3 and subjected to sintering at 650°C. for 5 hours in atmosphere, followed by sintering at 850° C. for 12hours. Thereafter, the same steps as in Example 21 were followed to givea powdery positive electrode active material.

COMPARATIVE EXAMPLE 21

In the same manner as in Comparative Example 20 except that lithiumcarbonate, aluminum oxide, cobalt oxide and scandium oxide were mixed inamounts as shown in Table 3, a powdery positive electrode activematerial was obtained.

COMPARATIVE EXAMPLE 22

In the same manner as in Comparative Example 20 except that lithiumcarbonate, cobalt oxide, stannic oxide, scandium oxide and manganesedioxide were mixed in amounts as shown in Table 3, a powdery positiveelectrode active material was obtained.

The atomic ratio of 0 in the positive electrode active materials asobtained in Examples 21-34 and Comparative Examples 11-22 was within therange of from 1.8 to 2.2 when Li was 1.

Preparation of Positive electrode

Using the positive electrode active materials obtained in Examples 21-34and Comparative Examples 11-22, positive electrodes were prepared as inthe following. A positive electrode active material (90 parts byweight), acetylene black (7 parts by weight) as a conductive material,polyvinilidene fluoride (PVDF, 3 parts by weight) as a binder andN-methyl-2-pyrrolidone (NMP, 97 parts by weight) as a solvent were mixedand stirred to give a paste. The paste was coated on a 20 μm thickcollector (aluminum sheet) with a doctor blade, dried and press-rolledto give 100 μm thick electrode sheet. A 12 mm diameter disc was punchedout from the electrode sheet and used as a positive electrode.

Preparation of Test Batteries

The above-mentioned positive electrode 11, a 25 μm thick, 16 mm diameterdisc separator 13 composed of a polypropylene film with fine pores, anda negative electrode 12 obtained by punching out a 15 mm diameter discfrom a 0.3 mm thick lithium sheet were overlapped in this order and setin a positive electrode can 15. Note that 14a and 14b are collectors ofpositive electrode 11 and negative electrode 12, respectively. Then, anelectrolyte solution obtained by dissolving 1 mole/L of lithiumperchlorate in propylene carbonate was injected into the positiveelectrode can 15. A negative electrode cap 16 was applied to thepositive electrode can 15, and the battery was sealed with an insulator17 (insulating gasket) to give a coin type lithium secondary batterysimilar to the one shown in FIG. 2.

EVALUATION TEST 2

Using the test batteries prepared using the positive electrode activematerials obtained in Examples 21-34 and Comparative Examples 11-22,charging and discharging were performed as in the following. Thebatteries were charged to 4.2 V using a 0.5 mA constant current. Afterone hours intermission, the batteries were discharged to 2.75 V using a0.5 mA constant current, followed by intermission for one hour. Such setof charging and discharging was taken as one cycle and charging anddischarging were repeated 100 cycles. The initial discharge capacity andcapacity retention ratio after 100 cycles of charging and discharging(ratio of discharge capacity after 100 cycles relative to the initialdischarge capacity) were determined. The results are shown in Tables 2and 3. In Tables 2 and 3, the initial discharge capacity is that per 1 gof positive electrode active material.

EXAMPLE 35

Using the positive electrode active material obtained in Example 21, apositive electrode was prepared as above. A negative electrode wasprepared in the following manner. In the same manner as in thepreparation of test battery above, a lithium secondary battery wasprepared.

Preparation of Negative Electrode

A mixture weighed to satisfy an atomic ratio ofLi:Ag:In:Zn:Fe:Te=60:15:45:38:4:1 was heated to 800° C. in a highly pureAr atmosphere (dew point temperature -60° C.) and melted for alloying.The alloy was pulverized to give a powdery negative electrode activematerial, from which a negative electrode was prepared in the followingmanner. The above-mentioned negative electrode active material (92 partsby weight), acetylene black (5 parts by weight) as a conductivematerial, ethylene-propylene-diene polymer (3 parts by weight) as abinder and xylene (97 parts by weight) as a solvent were mixed andstirred to give a paste. The paste was coated on a 10 μm thick collector(Cu sheet) with a doctor blade, dried and press-rolled to give a 50 μmthick electrode sheet. A 15 mm diameter disc was punched out from theelectrode sheet and used as a negative electrode.

EXAMPLE 36

In the same manner as in Example 35 except that a mixture was weighed tohave an atomic ratio of Li:Ag:Zn:Fe:Si:Te=60:15:70:4:9:1 and alloyed byheating the mixture to 750° C. in a similar atmosphere (highly pure Aratmosphere), a negative electrode and lithium secondary battery wereprepared.

EXAMPLE 37

In the same manner as in Example 35 except that a mixture was weighed tohave an atomic ratio of Li:Ag:Al:Si:Mn:Te=60:15:20:9:4:1 and alloyed byheating the mixture to 750° C. in a similar atmosphere (highly pure Aratmosphere), a negative electrode and a lithium secondary battery wereprepared.

EXAMPLE 38-41

In the same manner as in Example 35 except that the compositions were asshown in Table 4, negative electrodes and lithium secondary batterieswere prepared.

EVALUATION TEST 3

Using the test batteries obtained in Examples 35-41, the electromotiveforce was determined by a two-terminal network method. In addition, theabove-mentioned test batteries were subjected to charging anddischarging in the same manner as in the aforementioned Evaluation test2 to examine initial discharge capacity and capacity retention ratioafter 100 cycles of charge-discharge. Energy density at 50 cycles ofcharge-discharge was also determined. The results are shown in Table 4.

                  TABLE 2                                                         ______________________________________                                               Positive electrode                                                                          Lithium secondary battery                                       active material                                                                             Initial dis-                                                                            Cycle                                                 Atomic ratio  charge capa-                                                                            property*                                             Li  Ni     Al      P    city (mAh/g)                                                                          (%)                                    ______________________________________                                        Ex. 21   1     0.99   0.002 0.005                                                                              168     98                                   Ex. 22   1     1.00   0.002 0.005                                                                              156     98                                   Ex. 23   1     1.05   0.002 0.005                                                                              132     95                                   Ex. 24   1     0.97   0.002 0.005                                                                              157     97                                   Ex. 25   1     0.95   0.002 0.005                                                                              151     97                                   Ex. 26   1     0.90   0.002 0.005                                                                              144     95                                   Ex. 27   1     0.85   0.002 0.005                                                                              121     93                                   Ex. 28   1     0.99   0.001 0.005                                                                              150     97                                   Ex. 29   1     0.99   0.005 0.005                                                                              148     97                                   Ex. 30   1     0.99   0.010 0.005                                                                              120     95                                   Ex. 31   1     0.99   0.002 0.002                                                                              153     97                                   Ex. 32   1     0.99   0.002 0.007                                                                              155     98                                   Ex. 33   1     0.99   0.002 0.010                                                                              144     98                                   Ex. 34   1     0.99   0.002 0.020                                                                              120     95                                   Com. Ex.11                                                                             1     1.00   --    --   135     43                                   Com. Ex.12                                                                             1     1.10   0.002 0.005                                                                              77      88                                   Com. Ex.13                                                                             1     0.80   0.002 0.005                                                                              53      92                                   Com. Ex.14                                                                             1     0.99   --    0.005                                                                              135     80                                   Com. Ex.15                                                                             1     0.99   0.015 0.005                                                                              83      89                                   Com. Ex.16                                                                             1     0.99   0.002 --   140     71                                   Com. Ex.17                                                                             1     0.99   0.002 0.030                                                                              65      86                                   Com. Ex.18                                                                             1     1      --    --   101     30                                   ______________________________________                                         Note                                                                          *: capacity retention ratio after 100 cycles of chargedischarge          

                                      TABLE 3                                     __________________________________________________________________________    Positive electrode active material                                                                       Lithium secondary battery                          Atomic ratio               Initial discharge                                                                     Cycle property*                            Li       Ni Al Co Sn Sc Mn capacity (mAh/g)                                                                      (%)                                        __________________________________________________________________________    Com.Ex. 19                                                                          1  -- -- 1  -- -- -- 115     93                                         Com.Ex. 20                                                                          1.05                                                                             0.95                                                                             -- -- 0.042                                                                            0.002                                                                            -- 20      78                                         Com.Ex. 21                                                                          1.05                                                                             -- 0.084                                                                            0.95                                                                             -- 0.002                                                                            -- 106     56                                         Com.Ex. 22                                                                          1.05                                                                             -- -- 0.95                                                                             0.042                                                                            0.001                                                                            0.001                                                                            108     63                                         __________________________________________________________________________     Note                                                                          *: capacity retention ratio after 100 cycles of chargedischarge          

                                      TABLE 4                                     __________________________________________________________________________                            Litium secondary battery                              Negative electrode active material                                                                    Electro-                                                                           Energy                                                                            Initial dis-                                                                        Cycle                                  Composition of  Composition ratio                                                                     motive                                                                             density                                                                           charge capa-                                                                        property*                              alloy           (atomic ratio)                                                                        force (V)                                                                          (Wh/kg)                                                                           city (mAh/g)                                                                        (%)                                    __________________________________________________________________________    Ex. 35                                                                            Li--Ag--In--Zn--Fe--Te                                                                    60:15:45:38:4:1                                                                       4.1  170 350   ≧90                             Ex. 36                                                                            Li--Ag--Zn--Fe--Si--Te                                                                    60:15:70:4:9:1                                                                        4.0  165 340   ≧90                             Ex. 37                                                                            Li--Ag--Al--Si--Mn--Te                                                                    60:15:20:9:4:1                                                                        3.9  175 360   ≧90                             Ex. 38                                                                            Li--Ag--Sn--Fe--Te                                                                        60:24:36:4:1                                                                          4.0  165 340   ≧90                             Ex. 39                                                                            Li--Ag--In--Fe--Te                                                                        60:24:40:4:1                                                                          4.0  166 345   ≧90                             Ex. 40                                                                            Li--Ag--Sn--Zn--Fe--Te                                                                    60:24:40:2:2:1                                                                        4.0  171 320   ≧90                             Ex. 41                                                                            Li--Ag--Sn--Si--Fe--Te                                                                    60:24:40:2:2:1                                                                        4.0  162 330   ≧90                             __________________________________________________________________________     Note                                                                          *: capacity retention ratio after 100 cycles of chargedischarge          

The positive electrode active material for lithium secondary battery ofthe present invention composed of an oxide compound of the formula:LiNi_(w) Al_(x) P_(y) O_(z) wherein 0.80<w<1.10, 0<x<0.015, 0<y<0.03 and1.8≦z≦2.2 is economical and superior in the supply of starting materialsas compared with the positive electrode active material using LiCoO₂ andthe like. Using the inventive positive electrode active material, alithium secondary battery superior in capacity and cycle property can beobtained.

Since the lithium secondary battery of the present invention comprises apositive electrode comprising the above-mentioned positive electrodeactive material, it has high capacity, superior cycle property and canbe produced stably at low costs.

What is claimed is:
 1. A lithium secondary battery comprising a positiveelectrode composed of a positive electrode active material comprising anoxide compound comprising at least Li and Ni, and a negative electrodecomprising an Li--Ag--Te alloy.
 2. The lithium secondary battery ofclaim 1, wherein the positive electrode active material is composed ofan oxide compound of, besides Li and Ni, at least one member selectedfrom the group consisting of Co, Fe, Cr, V, Mn, P, Al, In, Sn, Ti, Cu,Ga, Ag and Zn.
 3. The lithium secondary battery of claim 1, wherein theatomic ratio of Li--Ag--Te alloy is Li:Ag:Te=10-120:1-20:0.001-2.
 4. Thelithium secondary battery of claim 1, wherein the negative electrode iscomposed of an Li--Ag--M1--M2--Te alloy wherein M1 is at least onemember selected from 3A, 4A and 5A group metals in the periodic table,and M2 is at least one member selected from transition metals except Ag.5. The lithium secondary battery of claim, 4, wherein the atomic ratioof the Li--Ag--M1--M2--Te alloy is Li:Ag:M1:M2:Te=10-120:1-30:1-100:1-30:0.001-2.